Moistureproof paper



, P 1936 L. E. BRANCHEN EITAL 2,036,392

7 MOI STUREPROOF PAPER Filed June 27, 1952 atente tthdhdht llieonard iE. hranchen and George lit. ilk, Rochester, N. T, assignors to East limit ilornpany, lltochester, N. T., a corporation at New Work Jill ilia.

This invention relates to moisture-proof paper. One object of our invention is to provide paper which is suficiently moisture-proof to' be used in wrapping many different substances, such as ioods, condiments, tobacco, chemicals, etc. which deteriorate through loss or absorption of moisture upon prolonged exposure to the atmosphere or when packaged in ordinary paper or cardboard. another object of our invention is to provide a process for producing such moisture-prooi'paper. Still another object is to provide paper which is both water-proof and grease-proof. Other ob jects will hereinafter appear.

At present there is a great demand for wrap-- ping materials which will prevent the loss or absorption of moisture by more or less perishable products, such as foods, tobacco, etc. which deteriorate when left in contact with the atmosphere. The wax paper of coerce, while waterresistant, allows water vapor to pass through its pores, and hence does not satisfy present-day requirements for many purposes. Furthermore, wax paper is not resistant to many kinds of greases. Also, when it hasa heavy coating of wax, the wax coating cracks readily. Moistureprcoi wrappings made by coating transparent sheets of regenerated cellulose or cellulose derivatives are widely used, but they are comparatively expensive.

We have discovered that ii paper is ping-=- nated with a solution (preferably a dilute solution) of wax, and then coated with a solution comprising nitrocellulose and a rather high proportion of a substantially water-cible plas! ticizer or softener, with or without a resin, a

. product is obtained which has very low moisture transmission, and is suitable for wrapping prodnote which are harmfully afiected by loss oi moisture to, or absorption of moisture from, the atmosphere. Glassine paper treated by our process gives an almost transparent product. Ordinary paper treated by our process, while not transparent, is glossy and shows a degree oi translucency depending on the character and thickness of the paper and the amount oi wax it contains. For packages in which transparency is not required, it is entirely suitable. Moreover,

it is less expensive than the transparent moistureprooi wrappings now on the market, so that it is available for wrapping products which sell at a very low price. Furthermore, our process may be used to produce moisture-proof printed paper,

from which very attractive packages can be prepared. In this case itis, of course, necessary to".

choose printing-inks which are not afiected by application We hit, 1932, Serial lilo. dllhlii'iii (er. hl-tiii the materials used in impregnating and coating the paper. This can readily be determined by test. in preparing printed moisture-proof paper we prefer, for the sake of economy, to impreg- 1 nate the paper with the wax first, then to print 5 it, and finally to coat it with the nitrocellulose solution. In this case eiiect of the wax solvent on the printing ink need not be taken into. consideration, as it will have evaporated before the printing takes place. We may, howto ever, print the paper first, then impregnate it with wax, and finally coat it with the nitrocellu lose solution.

Our process is applicable to any grade or thickness of paper, sized or unsized, and/or with va- 1a rious types or calendered surface, and even to light-weight cardboard. Paper or box-board containing wax which has been incorporated into the paper stock in the beater is improved in moisture-prooiness by being coated with our 2o nitrocellulose solutions.

In carrying out our invention, paper may be drawn through a solution of wax in a solvent. The solvents which we prefer to use are hydrocarbon solvents, such as petroleum naphtha, gasoline, benzene, toluene, etc. We have iound a petroleum naphtha with a boiling range from so" to 130? C. to be suitable. ong the waxes which we have found suitable for our process, are paramn, spermaceti, candelilla, and beeswax. so For instance, we may use that grade of para iii. a which melts at approximately 150 0. Solutions of waxes of low ,melting point, such as spermaceti, may be used at room temperature, whereas a solution of 150 C. paramn usually requires to be warmed before use. In the accompanying drawing iorg a part hcreoi,-

Fig. 1 is a diam a tic representation atone tom of apparatus for carrying out our invention.

Fig. 2 is a diagraatic representation, on an exaggerated scale, oi a cross-section voi our product.

in coercial practice it is convenient to use a continuous ersion hopper for impregnating the paper with the wax solution, as is she in t5 Figjl. The hopper is provided with heating means by which the wax solution may be kept warm. After being withdrawn from the wax solution, the paper is dried in warm air, for instance at a temperature of approtely C. 50 it is, of course, desirable to recover the solvent, by known methods.

While good moisture-proofing is obtained when our nitrocellulose solutions are coated on paper impregnated with wax solutions oiirom 1% to 50% concentration, and even when they are coated on paper which has been dipped in molten wax, there are many reasons for regarding wax concentrations of from 1% to 10%, approximately, as preferable. The most obvious, although not the most important of these reasons, is economy of material. Another is ease of coating. A more concentrated solution of parafiln gives a jelly which sets as it cools slightly in leaving the hopper, leaving a concentrated jell or film of paraflln on the surface of the paper, to which the nitrocellulose coating does not adhere well. Furthermore, when ahigh percentage of wax is used in impregnating the paper, the wax exudes through the nitrocellulose coating (giving a permanently taclw coating) when the latter is being dried, unless drying temperatures considerably above 50 C. are used, which, of course, is not desirable. We find 50 C. to be a satisfactory temperature for drying the paper both after the wax impregnation and after the coating when small percentages of wax are used. Such a temperature is both more economical and less dangerous in removing solvents than more elevated temperatures. If the wax exudes through the nitrocellulose coating, the appearance of the coating is mottled and streaked, and the paper fingerprints easily.

Moreover, when high wax concentrations are used, the adhesion of the nitrocellulose coating to the paper is impaired. For instance, when paper is impregnated with a 25% wax solution, and then coated with a nitrocellulose solution, it shows crease marks on folding, and the coating breaks away at the crease lines. If the paper is heated,

the coating strips off. These things are not true of papers which have been impregnated with low concentrations of wax and then coated with our nitrocellulose solutions.

None of the above disadvantages are evident when the concentration of the wax solution is about 10% or less. Above approximately 10% they begin to show up increasingly as the concentration of the wax solution is increased, and when the wax concentration approaches 20%, the disadvantageous properties accumulate to such an extent as to make the product undesirable, so that 20% may be regarded as the upper limit of wax concentration in the wax-impregnating solution which is permissible for even acceptable results. However, it will be apparent that for the best results approximately a 10% wax solution for impregnating the paper or approximately a 10% wax contentin the paper is the critical upper limit which we recommend.

In printing the wax-impregnated paper, prior to coating with the nitrocellulose solution, it is found ordinary printing ink prints very satisfac y on papers which have been impregnated with wax solutions of 10% or less concentration. When the wax concentration is increased above 10%, the printing begins to smear. the smearing increasing as the wax concentration is increased, until with paper which has been impregnated with a 50% wax solution, the printing rubs off completely when the finger is drawn across the paper.

When it is desired to glue our moisture-proof paper to labels, cardboard, etc., the nitrocellulose coating is applied on only one side of the waximpregnated paper, and the gluing is done on the non-coated side. In this case we have found that paper which has been impregnated with wax solutions of 10% or less wax concentration can be glued satisfactorily to cardboard, etc.,

aosasoe whereas papers impregnated with wax solutions of appreciably above 10% concentration do not show satisfactory adhesion.

We have found that when a 2% solution of high-melting paraflin in toluene is used for impregnating the paper, the wax deposited in the paper amounts to approximately 0.75% to 1.50% of the weight of the paper. When a 10% solution of wax is used, the wax deposited in the paper amounts to approximately 1.5% of the weight of the paper.

Instead of impregnating paper with a wax solution, we may incorporate wax into paper pulp in the beater in producing the paper. This latter may be accomplished in known manner by making a wax emulsion with the rosin size. Or we may incorporate a wax suspension into the paper pulp in the beater, and later flux the wax in the paper sheet. While the percentage of wax incorporated in the beater may be varied up to 10%, we have found that a proportion of approximately 3.5% of wax, calculated on the weight of the dry paper, gives a good product for our purposes.

After the paper has been impregnated with the wax, it is coated with a nitrocellulose solution containing a substantially water-immiscible plasticizer or softener, with or without a resin. Examples of the substantially water-immiscible softeners which we may. use are dibutyl phthalate,

tributyl phosphate, castor oil, diethyl phthalate,

diamyl phthalate, triphenyl phosphate, o-cresyl p-toluene sulfonate, and ethoxyethyl phthalate. Suitable resins for use in our nitrocellulose solutions are ester gum, cumarone and indene resins, glyptal resins, various types of phenol-formaldehyde resins, and natural resins, such, for instance, as sandarac. We prefer, however, to use a good grade of ester gum. As solvents for the nitrocellulose compositions we may use any combination of low-boiling solvents for nitrocellulose and the resin used, with or without the addition of hydrocarbon thinners. For instance we may use mixtures of ethyl acetate and ethyl alcohol in various proportions, with or without the addition of toluene, petroleum naphtha, or benzene, or we may use mixtures of ethyl alcohol and acetone, with or without toluene, etc. The amount of hydrocarbon thinner should not, of course, be so great as to precipitate the nitrocellulose from solution. We have found, however, that for the concentrations of nitrocellulose which we prefer to use, the solvent mixture may comprise at least 50% by weight of hydrocarbon thinner. Mediumboiling nitrocellulose solvents, such as diacetone alcohol or the monoethyl ether of ethylene glycol, may be added to the solvent mixtures to the extent of approximately 5 to 10% in order to prevent blushing. This is particularly desirable when dilute nitrocellulose solutions are used. While the hydrocarbon thinners are solvents for the waxes used in impregnating the paper, it is not necessary that a wax solvent be included in the solvent mixture used in making the nitrocellulose solutions. Nitrocellulose solvent mixtures consisting only-of acetone and alcohol or ethyl acetate and alcohol, which are non-solvents for waxes, give moisture-proofing results equal to those obtained when a hydrocarbon is contained in the nitrocellulose solvent mixture. A solvent mixture consisting of acetone and alcohol gives an odorless product, which is desirable for wrapping foods. The inclusion of hydrocarbons in the nitrocellulose solvent mixture, however, is desirable from the standpoint of economy. When the nitrocellulose solution comprises a resin, it is usually iii ,osasaa fer to use are approximately from 1% to 5% by weight when the paper is to be coatedby dipping, and approximately from 5% to 20% by weight when the coating is to be spread on the paper.

We have found that the best moisture-proofing is obtained when the weight of water-immiscible plasticizer used amounts to from about to about of the weight of nitrocellulose. We prefer to use approximately 75 parts by weight of plasticizer per parts by weight of nitrocellulose.

The proportion of resin in the nitrocellulose solution may be varied through a considerable range. We prefer to use proportions varying from about 15% to about 30% of the weight of nitrocellulose. The efiect of the resin in loweringthe moisture permeability of the paper, while usually appreciable, is not great compared with the effect of the water-immiscible plasticiaer. Its presence in the nitrocellulose coating contributes better gloss to the product, thus rendering the coated paper more attractive. Furthermore, a high degree of moisture-proofness is not always required in the coated paper. It may be desired to produce a paper which, while not particularly mois-. ture-proof, is water-proof and grease-proof. The wax paper of commerce, while water-proof, is not moisture-proof orresistant to many kinds of greases, such as petroleum greases. Paper impregnated with a wax solutionand then coated with a nitrocellulose solution containing a fairly low percentage of a substantially water-immiscible plasticizer, say from about 15% to about 40% oi plasticizer based on the weight of the nitro-, cellulose, together with from 15% to 30%, approximately, of ester gum, for instance, as in' Example 7 below, while not showing very low moisture permeability, is water-proof and greaseprooi, even to petroleum greases. Such paper has great utility for wrapping wet, greasy articles, a

or for protecting wrapped articles from water and grease. Whereas wax-impregnated papers coated with nitrocellulose solutions containing low percentages of plasticizer and no resin show a tendency to curl, the addition to the nitrocelluiose-plasticizer solution of a resin, for instance about 30% of ester gum, produces a paper which lies flat. v

After being coated with the nitrocellulose solution, the paper is again dried at a moderately elevated temperature, for instance at about 50 t1, the solvents being recovered in any known manner.

its examples of the solvent mixtures for the nitrocellulose which we have found useful, we give the iollowing:

Ethyl acetate 20 20 Ethyl alcohol 30 30 3O Acetone Toluene 50 Benezeno 50 Naphtha Nitrocellulose coatings such as we have described are transparent, glossy, and flexible, and

A non nro' One form of apparatus for carrying out our process is illustrated in Fig. l. The paper unwinds from a roll ll, passes over a guide roll it into a vat or hopper t in which a guide rollv 0 is immersed in a wax solution. The vat is provided with heating means. After passing under this guide roll i the paper passes between scraper bars 5 (if desired), over a guide roll 0, and through a drying chamber i kept at about 50 C. where the wax solvent is evaporated. Any

suitable solvent recovery system may be connected to the drying chamber. The wax-impregnated paper now passes to a coating machine such as is used in coating textiles in the manufacture oi artificial leather. This machine is provided with a hopper 0 and a doctor blade 0 which may form the front wall of the hopper. The nitrocellulose solution is deposited on the paper by the hopper and smoothed by the doctor blade, which can be adjusted so that any desired thickness may be given to the coating. The

coated paper passes through another drying chamber I10, which is maintained at about 50 C. and may also be provided with any suitable solvent recovery system. It a paper coated on only one side is desired, the paper-now goes to the wind-up. If a per coated on both sides is I to be produced, the paper is inverted after leaving the drying chamber it, for instance by passing over guide rolls ii and ii, and the other side of the paper is coated by a coating machine similar to the first, with hopper iii and doctor blade i0. litterv passing through a drying chamher it, preferably connected to a solvent recovery system, the paper goes to the wind-up 10. Other means for coating the wax-impregnated paper may also be used. For instance, the nitrocellulose solution may be sprayed onto the wax paper or the paper may be passed through the nitrocellulose solution; in the latter case the paper should not remain in the nitrocellulose solution for a period which will permit extensive attach of the solution upon the wax paper.

in testing papers for moisture permeability, we determine the number of milligrams of water vapor per hour per square centimeter transtted from a saturated atmosphere through the paper to a dehydrating agent. 'Moisture permeability is expressed in mg./hr./cm at 75 ii Wax impregnation alone has practically no efiect on the moisture permeability ot a paper. it plain paper with a moisture permeability or 0.50 showed, after impregnation with a 10% solution of par in petroleum naphtha, a moisture permeability of 0.57. A paper with a moisture permeability of 0.57 showed, .after impregnation with a 5% solution or spermaceti in petroleum naphtha, a moisture permeability oi 0.52.

Variations in the solvent used for the wax, and in the solvent mixture used in malring up iii tilt

the nitrocellulose solution, have no effect on the Y order of magnitude of the moisture permeability suchas Examples d, "l, 0 and 0, it was 0.002 inch thiclr. It is to be noted, however, that the illicit-- ness oi the paper does not appreciably ahiect the moisture permeability oi the iinal product. The wax impregnation did not appreciably increase the thiclrness or the paper. "li'he thiclrness oi the nitrocellulose coating on each side of the paper was approximately 0.001 inch.

Paper impgegnated Composition of nitrocelluwit 2 lose coating:

Example 5.--. beeswax -solu- Same as in Example 1.

tion in toluene.

Moisture permeability 0.008

Example 6..-. 5% candelilla wax Same as in Example 1.

. solution in toluene. Moisture permeability 0.018 Example 7..-. 5% spermaceti solu- 16 g. nitrocellulose.

tion in petroleum 4 g. dibutyl phthalete. naphtha. 2.4 g. ester gum in 84 g.

solvent A. Moisture permeability 0.183 Example 8..-. 5% spermoceti solu- Same as 111 Example 4.

tion in petroleum naphtha. Moisture permeability 0.0065 Example 9.... 6% spermaceti solu- 14 g. nitrocellulose.

tion in petroleum 10.5 g. dibutyl phthalate. naphtha. 4.2 g. ester gum 111 86 g.

. solvent A. Moisture permeability 0.0047 Example 10.-. 2% parafiln solution. 16 g. nitrocellulose.

2.4 g. dibutyl phtbalatc.

in 84 g. solvent D. Moisture permnbility 0.210. Example 11. 2% paraflin solution. 16 g. nitrocellulose 4.8 g. dibutyl phthalate in 84 g. solvent D. Moisture permeability 0.100 Example 12. 2% paraflin solution. 16 g. nitrocellulose 7.2 g. dibutyl phthalato in 84 g. solvent D.

Moisture permeability 0.022 Example 13. 2% parafiin solution. 16 g. nitrocellulose 12 g. dibutyl phthalate 84 g. solvent D.

Moisture permeability 0.008 Example 14. 2% paraffin solution. 16 g. nitrocellulose 16 g. dibutyl phthalate 84 g. solvent D.

From the above examples it will be seen that when wax-impregnated papers are coated with our nitrocellulose solutions their moisture impermeability is increased as much as 100 times or even more. It will also be seen that variations in the nature and concentration of the wax solutions used for impregnation of the paper do not affect the order of magnitude of the moisture permeability of the finished product. 0n the other hand, it will appear that the percentage of plasticizer in the nitrocellulose solution has a very appreciable effect on the moisture permeability of the product. We have found that other substantially water-immiscible plasticizers behave in about the same way as dibutyl phthalate: namely, they give maximum moistum-proofing when used in a. proportion of about 75% of theweight of the nitrocellulose. Coatings containing plasticizer in the proportion of 100% of the weight of the nitrocellulose, besides .being somewhat less'moisture-proof than those containing 75% of plasticizer, are somewhat soft and tend to be tacky.

While we prefer that the thickness of the dried nitrocellulose coating be approximately 0.001 inch on each side of the wax-impregnated paper, we may vary the thickness considerably. Thicker coatings give moisture-proofing as good as that obtained with the 0.001 inch coatings. Thinner coatings may also be used. For instance, when paper was impregnated with 2. 4% paraffin solution and given a 0.00025 inch coating, on one side only, of the nitrocellulose solution shown in Example 1, the moisture permeability of the product was 0.01. When the same thickness of coating was applied on both sides, the moisture permeability was 0.002.

One of the advantages of our moisture-proof papers is that their moisture-proofness is not materially lessened by abrading of the nitrocellulose coating. Some penetration of the nitrocellulose coating composition into the wax-impregnated paper appears to take place, even when neither the plasticizer nor any component of the solvent mixture used in the nitrocellulose coating composition is a, solvent for the wax.

Fig. 2 is a. diagrammatic representation of our product, the nitrocellulose coating being shown on only one side of the paper. 25 represents a sheet of paper, showing the fibers impregnated with wax. 23 represents a coating comprising nitrocellulose and a water-repellent plasticize 22 represents the penetration of the nitrocellulose composition into the wax-impregnated paper, merging of the nitrocellulose with the wax, at the interface thereof, being illustrated.

While we have referred particularly to the use oi. nitrocellulose in the overcoating, we may-use other cellulose derivatives, such, for instance, as

cellulose acetate, cellulose propionate, cellulose,

acetate-propionate, and cellulose ether, in case only moderate moisture-proofness is desired. We have not obtained with these other cellulose derivatives, moisture permeabilities of an order of magnitude as low as the best results obtained with nitrocellulose. For instance, when bond paper of 0.003 inch thickness, whose moisture permeability was 0.80, was impregnated with a 2% solution of paraflin and then coated with various cellulose derivatives, the results obtained were as follows. The coatings were 0.001 inch thick on each side of the paper.

Paper figfig I I Composition of coating:

Example 17. 2% paraihn solution. 20 g. cellulose acetate.

' 80 acetone.

Moisture permeability 0.19. I Example 18... 2% paraflln solution. 16 g. cellulose propionatc.

12 g. dibutyl phthalate in 84 g. oi a mixture of 90% ethylene dichloride and ethyl alcohol.

Moisture permeability 0.18.

Example 19... 2% paraflin solution. 16 g. cullulose ether.

' 12 g. dibutyl phthalate in 84 g. of a mixture of 67% toluene and 33% ethyl alcohol.

Moisture permeability 0.07.

SOme' decrease of moisture permeability is obtained by coating 9. wax-impregnated paper with a solution of nitrocellulose alone or with a solution of ester gum alone, but the moisture permeabilities obtained are not of the low order of magnitude obtained when a goodly percentage of a substantially water-immiscible plasticizer is usedv with the nitrocellulose. For instance when a. paper impregnated with a 5% solution g. dibutyl phthalate in.

iii

bit

of spermaoeti and having a moisture peeability of 0.52 is coated with a solution oi 10 g. of

nitrocellulose in 84 g. of solvent A, the moisture Moderate moisture-proofing is also obtained by I coating unimpregnated paper with our preferred nitrocellulose solutions. impregnating the paper with a resin in place of a wax and then coating with our preferred nitrocellulose solutions gives about the same moisture permeability as coating the unimpregnated paper. A paper whose moisture permeability was 0.57 was impregnated with a 20% solution of ester gum. The moisture permeability remained unchanged. After the resinimpregnated paper was coated with a solution of 10 g. of nitrocellulose, 12 g. of 'dibutyl phthalate .and 4.8g. oi ester gum in 8i g. of solvent A, it showed a moisture permeability of 0.16.

'll'hus it becomes apparent that we have discovered critical values for the combination of a nitrocellulose overcoating with wax-impregnated paper which are not at all apparent from any previous work in the art, and which give most exceptional results. While it was previously thought that for paper coated with wax only, the more wax loaded onto the paper the better the sheet, we have found that low wax values in the paper give exceptional results when overcoated with nitrocellulose solutions. While the prior art teaches the use of nitrocellulose lacquers for many purposes, we have found that in combination with wax paper containing low percentages of wax, a nitrocellulose solution gives unusual results and particularly so where our preferred range of plasticizers is employed. Other unusual departures of our invention from the teachings of the prior art will also be apparent.

In the claims, where we refer to wrapping paper this is, of course, intended to refer to any'packaging material of the general nature of paper whether it be tissue of approximately one thousandth of an inch in thickness, ordinary paper of 2 to 5 thousandths thickness, or whether it be carton board of several thousandths of an inch in thickness, such as 10, 20 or 30 thousandths of an inch or more.

What we claim as our invention and desire to be secured by Letters Patent of the United btates is:

1. A wrapping paper which is moisture-proof by reason of having, as moisture-proofing agents,

from 1% to of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose, from 45 to 85 parts by weight, approximately, of a substantially waterlmmiscible plasticizer, and from to 30 parts by weight, approximately, of a resin.

2. A wrapping paper. which is moisture-proof by reason of having, as moisture-proofing agents,

irom 1% to 10% of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose, from 45 to 85 parts by weight, approximately, of a substantially watercible plasticizer, and from 15 to 30 parts by weight, approximately, of ester gum.

3. A wrapping paper which is moisture-proof by reason of having, as moisture-proofing agents, from 1% to 10% of wax homogeneously dispersed therethrough, and a coating comprising 100 p by weight .of nitrocellulose and from A5 to 05 parts by weight, approximately, of a substantially water-immiscible plasticizer.

l. A wrapping paper which is moisture-prooi by reason of having, as moisture-proofing agents,

from 1% to 10% of wax homogeneously dispersed therethrough, and a coating comprising 100 p by weight of nitrocellulose and approximately 75 parts by weight oil a substantially water-immiscible plasticizer.

5. A wrapping paper which is moisture-prool by reason of having, as moisture-proofing agents, from 1% to 10% of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose and from A5 to 05 parts by weight, approximately, of dibutyl phthalate.

' 6. A wrapping paper which is moisture-proof by reason of having, as moisture-proofing agents, from 1% to 10% of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose and approximately 75 parts by weight of dibutyl phthalate.

7. A wrapping paper which is moisture-prooi' by reason of having, as moisture-proofing agents, from 2% to 5% of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose and approximately 75 miscible plasticizer.

8. Awrapping paper which is moisture-proof by reason of having, as moisture-proofing agents, from 2% to 5% of wax homogeneously dispersed therethrough, and a coating comprising 100 parts by weight of nitrocellulose and approximately 75 parts by weight of dibutyl phthalate.

9. A process of moisture-proofing wrapping paper which consists essentially in impregnating it with a 1% to 10% wax solution and subsequently coating it with a solution comprising 100 parts by weight oi nitrocellulose and from 45 to 85 parts by weight, approximately, of a substantially water-immiscible plasticizer.

10. A printed wrapping paper which is moisture-proof by reason of having, as moistureprooflng agents, from 1% to 10% of wax, based on the weight of the paper, contained therein, and a coating comprising 100 parts of nitrocellulose and from l5 to 85 parts, approximately, oi a substantially water-immiscible plasticizer.

11. A process of manufacturing a printed, moisture-proof wrapping paper which consists essentially in printing wax-impregnated paper containing from 1% to 10% of wax based on the weight of the paper, and subsequently coating it with a solution comprising 100 parts of nitrocellulose and from 45 to 85 parts by weight, approximately, of a substantially water-immiscible plasticlzer.

LEONARD E. BRANCHEN. GEORGE R. 

